1. Field of the Invention
The present invention relates to a traveling device for crawler type heavy equipment, which can prevent an abrupt change of a traveling speed when a traveling device and a working device are simultaneously operated in a crawler type excavator.
More particularly, the present invention relates to a traveling device for crawler type heavy equipment, which can improve the manipulability by preventing an abrupt decrease/increase of a traveling speed of the equipment so much that an operator can feel such an abrupt decrease/increase of the traveling speed when a combined operation, in which a left/right traveling device and a working device such as a boom are simultaneously driven, is performed.
2. Description of the Prior Art
As illustrated in FIG. 1, a conventional hydraulic circuit of a traveling device for heavy equipment includes first and second variable displacement hydraulic pumps 1 and 2 and a pilot pump 3 which are connected to an engine; a switching valve 5 for a left traveling motor and switching valves 6, 7, and 8 for working devices (e.g., a swing, a boom, an arm, and the like) which are installed in a first center bypass passage 4 of the first hydraulic pump 1; a switching valve 10 for a right traveling motor and switching valves 11 and 12 for working devices (e.g., a boom, a bucket, and an arm) which are installed in a second center bypass passage 9 of the second hydraulic pump 2; and a straight traveling valve 13 installed on an upstream side of the second center bypass passage 9, and shifted (in a right direction in the drawing), in response to a signal pressure from the pilot pump 3, to supply hydraulic fluid fed from the first hydraulic pump 1 to the switching valves 5 and 10 for the left and right traveling motors, respectively, and to supply hydraulic fluid fed from the second hydraulic pump 2 to the switching valves 6, 7, 8, 11, and 12 for the working devices, respectively.
In the drawing, reference numerals 14 and 15 denote left and right traveling pedals, and 16 and 17 denote joysticks for controlling the switching valves 6 and 11 for the working devices. A reference numeral 18 denotes a controller for outputting control signals to electro proportional valves 19 and 20 so as to control discharged flow rates of the first and second hydraulic pumps 1 and 2 by controlling inclination angles of swash plates of the first and second hydraulic pumps 1 and 2, and for outputting a control signal to an electric control valve 21 so that the signal pressure fed from the pilot pump 3 is supplied to the straight traveling valve 13. A reference numeral 26 denotes a main control valve (MCV).
The hydraulic fluid fed from the first hydraulic pump 1 is supplied to the switching valve 5 for the left traveling motor and to the switching valves 6, 7, and 8 for the working devices through the straight traveling valve 13. The hydraulic fluid fed from the second hydraulic pump 2 is supplied to the switching valve 10 for the right traveling motor and to the switching valves 11 and 12 for the working devices through the straight traveling valve 13.
On the other hand, in the case of simultaneously operating the left/right traveling device and the working device, the electric control valve 21 is shifted by the control signal inputted from the controller 18, and thus the straight traveling valve 13 is shifted in the right direction, as shown in the drawing, by the pilot signal pressure fed from the pilot pump 3 through a flow path 28.
Accordingly, the hydraulic fluid fed from the first hydraulic pump 1 is supplied to the switching valve 5 for the left traveling motor and to the switching valve 10 for the right traveling motor through the straight traveling valve 13.
The hydraulic fluid fed from the second hydraulic pump 2 is supplied to the switching valves 6 and 11 for the working devices through the straight traveling valve 13 and flow paths L1 and L2.
Accordingly, the hydraulic fluid fed from the first hydraulic pump 1 is supplied to the left/right traveling device of the equipment, and the hydraulic fluid fed from the second hydraulic pump 2 is supplied to the working devices of the equipment, so that the straight traveling performance of the equipment can be secured.
At this time, the hydraulic fluid discharged from the first hydraulic pump 1 is dividedly supplied to the switching valves 5 and 10 for the left and right traveling motors. That is, the flow rate is reduced by half to cause the traveling speed of the equipment also to be reduced by half, and thus an operator feels travel shock due to the reduction of the traveling speed.
As illustrated in FIG. 2, a conventional hydraulic circuit of a traveling device for heavy equipment includes first and second variable displacement hydraulic pumps 1 and 2 and a pilot pump 3 which are connected to an engine; a switching valve 5 for a left traveling motor and switching valves 6, 7, and 8 for working devices which are installed in a first center bypass passage 4 of the first hydraulic pump 1; a switching valve 10 for a right traveling motor and switching valves 11 and 12 for working devices which are installed in a second center bypass passage 9 of the second hydraulic pump 2; a straight traveling valve 13 installed on an upstream side of the second center bypass passage 9, and shifted (in a right direction in the drawing), in response to a signal pressure from the pilot pump 3, to supply hydraulic fluid fed from the first hydraulic pump 1 to the switching valves 5 and 10 for the left and right traveling motors, respectively, and to supply hydraulic fluid fed from the second hydraulic pump 2 to the switching valves 6, 7, 8, 11, and 12 for the working devices, respectively; and a fixed orifice 23 installed in a confluence passage 22 for connecting in parallel a flow path L2 branched from the upstream side of the second center bypass passage 9 and the second center bypass passage 9, the fixing orifice 23 supplying a part of the hydraulic fluid fed to the working device to the traveling device, when the traveling device and the working device are simultaneously operated, to prevent an abrupt reduction of a traveling speed.
In the drawing, a reference numeral 24 denotes a check valve installed in the confluence passage 22.
Since the above-described construction, except for the fixed orifice 23 and the confluence passage 22 in which the check valve 24 is installed, is substantially the same as the construction as illustrated in FIG. 2, the detailed description thereof will be omitted. In the following description of the present invention, the same drawing reference numerals are used for the same elements across various figures.
Accordingly, in the case of simultaneously driving the left/right traveling device and the working device, a part of the hydraulic fluid fed from the second hydraulic pump 2 to the working device through the flow path L2 is supplied to the traveling device through the confluence passage 22, and thus the abrupt reduction of the traveling speed can be prevented.
At this time, if load pressure generated on the working device side is higher than load pressure generated on the traveling device side (e.g., in the case of pulling-up operation), most hydraulic fluid discharged from the second hydraulic pump 2, which should be supplied to the working device) is supplied to the traveling device through the confluence passage 22.
Accordingly, the working device is not driven, but the traveling speed is abruptly increased, so that the manipulability of the equipment is lowered, and thus an operator may instantaneously make erroneous manipulation.